Phase detector, timing recovery device using the same, and a...

Details Phase detector, timing recovery device using the same, and a... Phase detector, timing recovery device using the same, and a...

1999-07-30

2002-07-02

Vo, Don N. (Department: 2631)

Pulse or digital communications

Receivers

Angle modulation

C375S326000, C375S327000, C375S329000, C375S355000, C375S373000, C375S375000, C375S376000, C329S307000, C329S346000, C329S306000

Reexamination Certificate

active

06415004

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a phase detector used for various types of digital Communications such as satellite communications or mobile communications and capable of realizing rapid timing phase synchronization within a preamble and low phase-timing jitter in a data section and also capable of promoting reduction of a size and a weight of a device. This invention also relates to a timing recovery device which uses the phase detector, and a demodulator which uses the timing recovery device.
BACKGROUND OF THE INVENTION
As a timing recovery device in a demodulator for digital radio communications based on the conventional technology, there is a feedback type of device which detects advance or delay in phase from the information on the absolute value of phase data whose difference has been taken as described in the reference “Timing Recovery Scheme Using Received Signal Phase Information for QPSK Modulation” (by Fujimura, in Proceedings of Electronic Information Communication Association, Vol. J81-B-II No. 6, pp.665-668, June, 1998).
FIG. 22
is a block diagram showing a general configuration of a receiver containing a demodulator having a timing recovery device based on the conventional technology. As shown in
FIG. 22
, an antenna
101
receives RF signal containing a QPSK demodulation signal, and a frequency converting section
102
outputs a baseband signal comprising an in-phase component and an orthogonal component by successively subjecting this RF signal to amplification, band restriction, and frequency conversion.
A/D converter
111
a
samples the in-phase component and an A/D converter
1116
samples the orthogonal component of the baseband signal at each time t=&tgr;+iT/2. The A/D converter
111
a
outputs the sampled data array I
i
(in-phase amplitude component) and while the A/D converter
111
b
outputs sampled data array Q
i
(orthogonal amplitude component). Herein T indicates a symbol duration and &tgr; indicates a timing error in a range of −T/2≦&tgr;≦2. Here i is a natural number such as 1, 2, 3 . . . It should be noted that sampling of a baseband signal by the A/D converters
111
a,
111
b
is executed in a first transitional edge of a sampling clock SSK outputted from a timing recovery section
112
described later.
A coordinate transform section
110
computes a baseband signal phase data array &thgr;
i
by executing coordinate transformation, namely inverse tangent computing using the data array I
i
and Q
i
outputted from the A/D converters
111
a,
111
b
respectively.
 &thgr;
i
=tan
−1
.(
Q
i
/I
i
)  (1)
A timing recovery section
112
executes phase control, namely timing recovery processing for generating a sampling clock SSK and a recovered symbol clock RRC each phase-synchronized with the inputted baseband signal using the phase data array &thgr;
i
outputted from the coordinate transform section
110
.
Nyquist data extracting section
113
extracts a data array at an Nyquist point using the recovered symbol clock RRC from the data arrays I
i
and Q
i
sampled with the sampling clock SSK. A data determining section
116
determines data according to the data arrays at the Nyquist point, and outputs the data as demodulated data to a decoder
104
. The decoder
104
executes decode processing according to the demodulated data. It should be noted that data determination by the data determining section
116
is executed based on a coherent detection scheme or a differential detecting scheme compatible with the modulating system.
Herein detailed description is made for the timing recovery processing by the timing recovery section
112
by referring to
FIG. 23
to FIG.
25
A. Herein description is made for a case when a bust signal comprising a preamble section used for timing recovery or the like and a data section including a message as a random pattern is received.
FIG. 23
is a view showing temporal change in the phase &thgr;(t) of a baseband signal when a 0&pgr; demodulated signal repeating a phase fluctuation of ±180 (degree) for one symbol is received and a temporal change in the absolute signal &agr;(t) of deviation for T/2 of this phase &thgr;(t) (½ of symbol duration).
FIG. 24
is a view showing a temporal change in the phase &thgr;(t) of the baseband signal when a random pattern of a data section in which the phase &thgr;(t) changes at random is received and a temporal change of an absolute signal &agr;(t) of deviation for T/2 of this phase &thgr;(t). FIG.
25
A and
FIG. 25B
are constellation views showing amplitude shift of a baseband signal at a Nyquist point. In these figures the horizontal axis indicates an in-phase component (I channel) of a baseband signal, while the vertical axis indicates an orthogonal component (Q channel) of the baseband signal.
FIG. 25A
is a constellation view showing a state when there is no DC offset, and
FIG. 25B
is a constellation view showing a state where DC offset is added.
The preamble signal shown in
FIG. 23
is a signal alternately shifting at the point A or the point C in
FIG. 25A
, while the random pattern signal shown in
FIG. 24
is a signal shifting at random at any point between the points A and D in FIG.
25
A. In otherwords, the phase &thgr;(t) of the preamble signal shown in
FIG. 23
repeats fluctuation of 180 degrees in one symbol duration, and the &thgr;(t) of the random pattern signal shown in
FIG. 24
repeats fluctuations of 0, ±90, ±180 degrees in one symbol duration. It should be noted that the time t=0, T, 2T, 3T, . . . on the time axis indicates a Nyquist point, and that t=0 indicates arrival of the first burst signal. T indicates a symbol duration.
An absolute value signal &agr;(t) of a deviation of T/2 time is defined by the following equation (2).
&agr;(
t
)=min [|&thgr;(
t
)−&thgr;(
t−T/
2)|, 360−|&thgr;(
t
)−&thgr;(
t−T/
2)|]  (2)
This absolute value signal &agr;(t) is a signal obtained based on the fact that the change in the phase &thgr;(t) is rather moderate around the Nyquist point (t=0, T, 2T, 3T, . . . ) and is sharp around points at T/2 symbol time after the Nyquist point (t=T/2, 3T/2, 5T/2, 7T/2, . . . ). The absolute value signal &agr;(t) shown in FIG.
23
and
FIG. 24
includes a symbol frequency component s(t) and a DC component as shown in the following equation (3) whether or not the signal is a preamble signal or a random pattern signal. Namely, the signal &agr;(t) includes a symbol frequency component
s
(
t
)=−sin 2&pgr;
t/T
  (3)
and a DC component. Especially, when a preamble signal is received, lot of symbol frequency components s(t) are included in the signal &agr;(t).
Herein a difference signal &Dgr;&agr;(t) for the absolute value signal &agr;(t) with ½ symbol time interval is defined as indicated by the following equation:
&Dgr;&agr;(
t
)=&agr;(
t
)−&agr;(
t−T/
2)  (4)
Following relation exists between an average value M[&Dgr;&agr;(ta)] of this difference signal &Dgr;&agr;(t) at the time ta=&tgr;+jT and the timing error &tgr;. Herein, j is a natural number such as 1, 2, 3 . . .
when
M
[&Dgr;&agr;(
ta
)]<0 then 0<&tgr;<
T/
2
when
M
[&Dgr;&agr;(
ta
)]>0 then −
T/
2<&tgr;<0  (5)
It should be noted that, when M[&Dgr;&agr;(ta)] is equal to zero, &tgr; is also equal to zero.
Similarly the following relation as expressed by the equation (6) exists between the average value [&Dgr;&agr;(t)×(−1)
i
] of values each obtained by multiplying the difference signal &Dgr;&agr;(t) at the time tb=&tgr;+iT/2 and the timing error &tgr;:
when
M
[&Dgr;&agr;(
tb
)×(−1)
i
]<0 then 0<&tgr;<
T/
2
when
M
[&Dgr;&agr;(
tb
)×(−1)
i
]>0 then −
T/
2<&tgr;<0  (6)
It should be noted that when M[&Dgr;&agr;(

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